1. Field of the Invention
The present invention relates to a locking device for a seat suspension in a vehicle seat.
2. Description of the Prior Art
Conventionally, in many of vehicle seats, especially the driver's seats, there is provided a seat suspension between the seat and the floor of the vehicle so that the seat can be maintained at a predetermined height level even when an occupant different in weight from an ordinary occupant is seated thereon, and also that vibrations produced during driving can be absorbed to improve the sitting feeling of the occupant. However, during running on bad roads or the like, such conventional seat suspension may rather cause the seat to vibrate excessively, which interferes with the occupant in driving operations. In order to solve this, there are proposed various kinds of seat suspensions each provided with a locking device which is capable of stopping the suspension function thereof as occasion demands, e.g., as disclosed in Japanese Patent Publication No. 144139 of 1982.
Specifically, the above-mentioned seat supension with a locking device, as shown in FIG. 7, comprises a lower frame (1) fixed to the floor side and an upper frame (2) attached to the seat proper S and supported resiliently to the lower frame (2) by means of X-shaped links (3) (4). The locking device comprises an engagement pin (5) provided in the upper frame (2) and a lock plate (6) journalled to the lower frame (1) correspondingly to the engagement pin (5), whereby the lock plate (6) can be engaged with the engagement pin (5) due to the biasing forces of a tension spring (7) to stop the suspension function of the suspension.
However, in the locking device of such conventional seat suspension, since the engagement of the lock plate (6) with the engagement pin (5) is retained only by the biasing forces of the tension spring (7), when excessive loads or heavy shocks are applied to the upper frame (2), there is a possibility of the engagement of the lock plate (6) with the engagement pin (5) being removed unexpectedly. Thus, such prior art locking device may cause the occupant uneasiness when the occupant is going to sit down onto the seat, that is, it lacks reliability in such time.